The short answer
An air source heat pump works like a fridge in reverse: it absorbs heat from the outside air (even when it's cold), compresses it to raise the temperature, and transfers it to your home's radiators, underfloor heating and hot water. Because it moves heat rather than burning fuel, it typically delivers around 3 units of heat for every unit of electricity it uses. It runs at a lower flow temperature than a gas boiler, which is why system design and radiator sizing matter.
Understanding that a heat pump moves heat rather than generating it is the key to understanding both its efficiency and why a good install matters so much.
The components
- Outdoor unitextracts heat from air
- Compressorraises the temperature
- Heat exchangertransfers heat indoors
- Hot water cylinderstores domestic hot water
- Controlsmanage flow temperature
The cycle, step by step
- Absorb: a refrigerant in the outdoor unit absorbs heat from the outside air.
- Compress: a compressor raises the refrigerant's temperature.
- Transfer: a heat exchanger passes that heat to your heating water.
- Distribute: radiators or underfloor heating warm the home; a cylinder stores hot water.
Why flow temperature matters
Heat pumps are most efficient running at a lower flow temperature than a gas boiler — warming your home steadily rather than blasting heat. That's why a good installer sizes radiators and designs the system for low-temperature operation; an undersized or badly designed system forces the pump to work harder and run more expensively.
Get a system designed for your home
We'll match you with an MCS-certified installer who carries out a heat-loss survey and designs the system for efficient low-temperature running.
Frequently asked questions
Do heat pumps work below freezing?
Yes — air source heat pumps extract heat from the air even in sub-zero temperatures, though efficiency falls as it gets colder. Correct sizing for your home's heat loss is what matters most.
Why is a heat pump efficient?
Because it moves existing heat from the outside air rather than burning fuel to create it. It typically delivers around 3 units of heat for each unit of electricity used.
Do I need new radiators?
Sometimes. Heat pumps run at a lower flow temperature than boilers, so some radiators may need upsizing. A heat-loss survey identifies which, if any.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.